The present invention relates to a cooling apparatus for electronic components, such as a transistor for a power supply circuit. Particularly, it relates to an electronic component cooling system which has sufficient coolability, even when a heat radiating portion having a plate fin type radiator is spaced apart from the electronic component, and has high flexibility in design.
Recently, the integration and installation density of electronic components have been increasingly higher. Accordingly improvement in cooling efficiency of the electronic components has become more important. Especially, so called power ICs, such as an IGBT (Insulated Gate type Bipolar Transistor), are not only used for signal transfer but also for supplying drive power to other components, so that they produce a large amount of heat. Thus, it is difficult to cool them.
FIG. 10 is a schematic perspective view of a conventional air-cooled electronic components cooling apparatus 501.
In this conventional example, four printed boards 519 having electronic components mounted thereon (Integrated Circuits and the like, not shown) are arranged in parallel. At each top and bottom end of the boards 519, a plate-fin type radiator 5 (a heat radiating portion) 511, 515 is disposed. Each of the plate-fin type radiators 511, 515 has honeycomb shaped vent holes 511a and 515a, through which air flows in the arrow direction in FIG. 10. Most of the heat produced by the elements on the boards 519 is transferred through the boards 519 and then to the plate-fin type radiators 511, 515 and finally to be radiated into the outside air. In order to improve the heat conduction through the boards 519, an aluminum plate (not shown) may be embedded in the boards.
In the conventional electronic component cooling apparatus shown in FIG. 10, the plate-fin type radiator 511,515 has to be disposed around the boards 519 and in contact with the boards 519. So, flexibility in design is poor, and because of the large volume of the plate-fin type radiator 511, 515, the whole apparatus becomes bulky.
When improvement in the coolability is required, in a case where the size of the whole apparatus is limited, it is necessary to increase the air flow (enlarging the size of a fun or increasing the rotation speed of the fun, or the like). That is because, in most cases, there is little probability to decrease the temperature at the radiator inlet portion, and there is a limit in improving the efficiency of the radiator itself. Under the condition where it is impossible to increase the air flow, the volume or size of the radiator has to be increased to enlarge the whole apparatus volume. Thus, in the above case, design flexibility is poor.
FIG. 11 is a schematic side-sectional view of a conventional water-cooled electronic component cooling apparatus 401.
In this conventional example, a water-cooled heat exchanger 611 is disposed around boards 619. In the water-cooled heat exchanger 611, a honeycomb shaped water conduit 611a is formed within which a cooling water (coolant) flows.
The water-cooled electronic component cooling apparatus shown in FIG. 11 has large a heat transfer capacity and has a higher coolability than the air-cooled apparatus shown in FIG. 10. However, the water-cooled electronic component cooling apparatus of FIG. 11 requires a water-cooling facility, such as a circulation pipe line for cooling water, a heat exchanger, and the like. So, since the apparatus becomes large and complicated and the system configuration requires more elements than the air-cooled type, the whole facility of the water-cooling system becomes complicated.
And, when improvement in coolability is required, in a case where the size of the whole apparatus is limited, it is necessary to increase the water flow (enlarging the size of a pump or increasing the rotation speed of the pump, or the like). This is because, in most cases, there is little probability to decrease the temperature at the radiator inlet portion, and there is a limit in improving the efficiency of the radiator itself. Under the condition where it is impossible to increase the water flow, the volume of the radiator has to be increased to thereby enlarge the whole apparatus. Thus, like the air-cooled type, design flexibility is also poor.
In view of the above problems, the object of the present invention is to provide an electronic component cooling apparatus which has sufficient coolability even when the heat radiating portion having a plate-fin type radiator is spaced apart from an electronic component, and which has high design flexibility.
In order to solve the above-mentioned problems, a cooling apparatus according to the present invention, for cooling an electronic component or boards on which the electronic component is mounted, comprises an air-cooled or water-cooled heat radiating portion and a meandering capillary tube heat pipe arranged to transfer heat between the above-mentioned electronic component or the board and the heat radiating portion.
Meandering capillary tube heat pipes have a very large heat transfer capability and are able to transfer heat along a long distance with a low thermal resistance. Therefore, even when the distance between the heat radiating portion and the electronic component or the board on which the electronic component is mounted becomes long, the temperature rise of the electronic component and the like can be suppressed. Therefore, it is possible to separate the board apart from the heat radiating portion, thus improving flexibility in arrangement of the electronic component or the heat radiating portion, so that various shaped apparatus can be designed and manufactured. And, a higher-density mounting of electronic components (Integrated Circuits and the like) is achieved and thus miniaturization of the apparatus is achieved.
In this specification, the term meandering capillary tube heat pipe means a heat pipe which has the following characteristics (disclosed in Japanese Laid-open Patent Publication No. Hei 4 (1992)-190090(U.S. Pat. No. 5,219,020 (Jun. 15,1993)), the entire contents of which are incorporated herein by reference).
(1) The meandering capillary tube heat pipe comprises a capillary that is sealed off from the outside.
(2) One part of the capillary acts as a heat radiating portion, and another part acts as a heat receiving portion.
(3) The heat receiving portion and the heat radiating portion are alternately arranged, and between them the capillary meanders.
(4) In the capillary, a two-phase condensable working fluid is sealed.
(5) The capillary has a diameter less than a maximum diameter which allows the two-phase condensable working fluid to circulate and move while being sealed inside of the capillary.
Examples of this type of meandering capillary tube heat pipe are disclosed in Japanese Laid-open Patent Publication No. Hei 4 (1992)-190090 (U.S. Pat. No. 5,219,020 (Jun. 15,1993)), No. Hei 7 (1995)-63487 (U.S. Pat. No. 5,697,428 (Dec. 16,1997)) and No. Hei 9 (1997)-49692 (U.S. Pat. No. 5,737,840 (Apr. 14, 1998)). Among them, in the latter two Japanese Patent Publications, the meandering capillary is embedded in a comparatively thin flat plate (thus called a plate-type heat pipe). If such a plate type heat pipe is adapted, it is easy to design and assemble connecting portions with a board and a heat radiating portion (a plate-fin type radiator and the like). The plate type heat pipe disclosed in Japanese Laid-open Patent Publication No. Hei 9 (1997)-49692(U.S. Pat. No. 5,737,840 (Apr. 14,1998)) uses, as a material, an aluminum extruded material which has many small channels, thereby reducing the material cost and machining cost.
In the electronic component cooling apparatus according to the present invention, it is preferable that the heat radiating portion comprises a set of radiation fins with an outer-shape of a substantially flat plate (plate fin type radiator)and the meandering capillary tube heat pipe comprises a plate type heat pipe with an outer-shape of a substantially flat plate and connected along the heat radiating portion.
Since the meandering capillary tube heat pipe is connected along the heat radiating portion, a wide contact area between the heat pipe and the heat radiating portion may be retained to reduce the thermal resistance through the contacting portion between them.
Instead of the plate fin type radiator, a hedgehog-type heat sink made by TS Heatronics Co., Ltd. (Japanese Laid-open Patent Publication No. Hei 5 (1993)-315482 (U.S. Pat. No. 5,507,092 (Apr. 16,1996))) may be used.
The electronic component cooling apparatus according to an aspect of the present invention, for cooling a plurality of boards on which electronic components are mounted, the boards being arranged in a row, comprises a plate fin type air-cooled or water-cooled radiator and a plate type meandering capillary tube heat pipe that transfers heat between an end face of the boards and the heat radiator. The meandering capillary tube heat pipe has one part constituting a sidewall of the electric component cooling apparatus and another part bent at the end of the sidewall and connected along the heat radiating portion.
According to this aspect of the electronic component cooling apparatus, even when the electronic component mounting board is spaced apart from the heat radiating portion, a temperature rise of the electronic component can be prevented. Thus it is possible to sufficiently cool the electronic components while improving the installation density of the electronic components.
In the electronic component cooling apparatus according to the present invention, it is preferable that the thermal resistance at the connecting portion (contacting face) between the heat radiating portion and the meandering capillary tube heat pipe is between 0.001xc2x0 C./W and 3.00xc2x0 C./W, and the heat flux of the same is between 0.01 W/cm2 and 30 W/cm2.
In this range, while the temperature rise at the connecting portion between the heat pipe and the heat radiating portion is suppressed under a certain temperature, sufficient heat transfer can be achieved. The range of the thermal resistance on the same area is more preferably between 0.01xc2x0 C./W and 0.5xc2x0 C./W, and the range of the heat flux of the same area is preferably between 0.01 W/ cm2 and 10 W/ cm2.
In the electronic component cooling apparatus according to the present invention, it is preferable that the thermal resistance at the contacted portion between the end face of the board and the meandering capillary tube heat pipe is between 0.001xc2x0 C./W and 3.00xc2x0 C./W, and the heat flux of the same is between 0.01 W/ cm2 and 30 W/ cm2.
In this range, while the temperature rise at the contacting portion between the end face of the board and the meandering capillary tube heat pipe is suppressed under a certain temperature, sufficient heat transfer can be achieved. The range of the thermal resistance on the same portion is preferably between 0.01xc2x0 C./W and 0.5xc2x0 C./W, and the heat flux of the same portion is preferably between 0.01 W/ cm2 and 10 W/cm2.
In an electronic component cooling apparatus according to the present invention, a bracket is preferably provided which secures the board between the end face of the board and the meandering capillary tube heat pipe. The bracket is preferably secured to the heat pipe by solder and/or a screw.
When the board is mounted to the heat pipe firmly, the heat transfer from the board to the heat pipe is improved.
In an electronic component cooling apparatus according to the present invention, it is preferable that the meandering capillary tube heat pipe is secured to the plate fin type radiator by a screw, and a screw-threaded hole (female screw thread) is formed in the plate-fin type radiator. The female screw thread is preferably formed in a lock insert which is installed to the radiator.
As a material used for these cooling apparatuses, aluminum (and alloys thereof), which has good heat transfer efficiency and machinability and is light, is preferably used. However, conventional aluminum is relatively soft and is easily damaged, when the female screw thread is formed into the aluminum. In such case, the screw thread can not be firmly tightened with another part. In such a case, the heat transfer between both parts is so poor as to produce a disadvantageous thermal resistance. To overcome this problem, the female screw thread is formed into a lock insert, which is inserted into the plate fin type radiator. Using this technique, the screw can be firmly tightened so that the meandering capillary tube heat pipe can be securely contacted with the plate fin type radiator, and disadvantageous high thermal resistance can be removed.
According to another aspect of the present invention, an electronic component cooling apparatus is provided with an air-cooled or water-cooled radiator and a meandering capillary tube heat pipe to carry out heat transfer between the board and the radiator. The meandering capillary tube heat pipe is attached along a surface of the board.
According to this aspect of the invention, the heat produced from the board is removed by the heat pipe, which is Just located reverse of the board, so that it does not need to transfer the heat for the long distance through the board, which thermal conductivity is generally low. Thus, this arrangement has good coolability.